fix(zathura): use absolute path for matugen config and ensure file exists

- Updated 'extraConfig' to use an absolute path for the 'zathura-matugen'
  include, fixing path resolution issues.
- Added a home activation script to create an empty 'zathura-matugen' file
  if it doesn't exist, preventing zathura from crashing on fresh installs
  before matugen has run.

apps/zathura/default.nix

@@ -1,4 +1,4 @@
-{ pkgs, ... }:
+{ pkgs, config, lib, ... }:
 {
   programs.zathura = {
     enable = true;
@@ -12,9 +12,15 @@
       zoom-min = 10;
       recolor = true;
     };
-    extraConfig = "include zathura-matugen";
+    extraConfig = "include ${config.home.homeDirectory}/.config/zathura/zathura-matugen";
   };
 
+  home.activation.createZathuraMatugen = lib.hm.dag.entryAfter ["writeBoundary"] ''
+    if [ ! -f "${config.home.homeDirectory}/.config/zathura/zathura-matugen" ]; then
+      touch "${config.home.homeDirectory}/.config/zathura/zathura-matugen"
+    fi
+  '';
+
   xdg.mimeApps = {
     enable = true;
     defaultApplications = {